diff --git a/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaUtil.java b/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaUtil.java
index e6cbac8716..b35b1c8b4c 100644
--- a/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaUtil.java
+++ b/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaUtil.java
@@ -15,13 +15,17 @@
  */
 package com.google.android.exoplayer2.ext.ima;
 
+import static com.google.android.exoplayer2.util.Assertions.checkArgument;
 import static com.google.android.exoplayer2.util.Assertions.checkNotNull;
 import static com.google.android.exoplayer2.util.Assertions.checkState;
+import static com.google.android.exoplayer2.util.Util.sum;
+import static java.lang.Math.max;
 
 import android.content.Context;
 import android.os.Looper;
 import android.view.View;
 import android.view.ViewGroup;
+import androidx.annotation.CheckResult;
 import androidx.annotation.Nullable;
 import com.google.ads.interactivemedia.v3.api.AdDisplayContainer;
 import com.google.ads.interactivemedia.v3.api.AdError;
@@ -263,6 +267,92 @@ import java.util.Set;
     }
   }
 
+  /**
+   * Expands a placeholder ad group with a single ad to the requested number of ads and sets the
+   * duration of the inserted ad.
+   *
+   * <p>The remaining ad group duration is propagated to the ad following the inserted ad. If the
+   * inserted ad is the last ad, the remaining ad group duration is wrapped around to the first ad
+   * in the group.
+   *
+   * @param adGroupIndex The ad group index of the ad group to expand.
+   * @param adIndexInAdGroup The ad index to set the duration.
+   * @param adDurationUs The duration of the ad.
+   * @param adGroupDurationUs The duration of the whole ad group.
+   * @param adsInAdGroupCount The number of ads of the ad group.
+   * @param adPlaybackState The ad playback state to modify.
+   * @return The updated ad playback state.
+   */
+  @CheckResult
+  public static AdPlaybackState expandAdGroupPlaceholder(
+      int adGroupIndex,
+      long adGroupDurationUs,
+      int adIndexInAdGroup,
+      long adDurationUs,
+      int adsInAdGroupCount,
+      AdPlaybackState adPlaybackState) {
+    checkArgument(adIndexInAdGroup < adsInAdGroupCount);
+    long[] adDurationsUs =
+        updateAdDurationAndPropagate(
+            new long[adsInAdGroupCount], adIndexInAdGroup, adDurationUs, adGroupDurationUs);
+    return adPlaybackState
+        .withAdCount(adGroupIndex, adDurationsUs.length)
+        .withAdDurationsUs(adGroupIndex, adDurationsUs);
+  }
+
+  /**
+   * Updates the duration of an ad in and ad group.
+   *
+   * <p>The difference of the previous duration and the updated duration is propagated to the ad
+   * following the updated ad. If the updated ad is the last ad, the remaining duration is wrapped
+   * around to the first ad in the group.
+   *
+   * <p>The remaining ad duration is only propagated if the destination ad has a duration of 0.
+   *
+   * @param adGroupIndex The ad group index of the ad group to expand.
+   * @param adIndexInAdGroup The ad index to set the duration.
+   * @param adDurationUs The duration of the ad.
+   * @param adPlaybackState The ad playback state to modify.
+   * @return The updated ad playback state.
+   */
+  @CheckResult
+  public static AdPlaybackState updateAdDurationInAdGroup(
+      int adGroupIndex, int adIndexInAdGroup, long adDurationUs, AdPlaybackState adPlaybackState) {
+    AdPlaybackState.AdGroup adGroup = adPlaybackState.getAdGroup(adGroupIndex);
+    checkArgument(adIndexInAdGroup < adGroup.durationsUs.length);
+    long[] adDurationsUs =
+        updateAdDurationAndPropagate(
+            Arrays.copyOf(adGroup.durationsUs, adGroup.durationsUs.length),
+            adIndexInAdGroup,
+            adDurationUs,
+            adGroup.durationsUs[adIndexInAdGroup]);
+    return adPlaybackState.withAdDurationsUs(adGroupIndex, adDurationsUs);
+  }
+
+  /**
+   * Updates the duration of the given ad in the array and propagates the difference to the total
+   * duration to the next ad. If the updated ad is the last ad, the remaining duration is wrapped
+   * around to the first ad in the group.
+   *
+   * <p>The remaining ad duration is only propagated if the destination ad has a duration of 0.
+   *
+   * @param adDurationsUs The array to edit.
+   * @param adIndex The index of the ad in the durations array.
+   * @param adDurationUs The new ad duration.
+   * @param totalDurationUs The total duration the difference of which to propagate to the next ad.
+   * @return The updated input array, for convenience.
+   */
+  /* package */ static long[] updateAdDurationAndPropagate(
+      long[] adDurationsUs, int adIndex, long adDurationUs, long totalDurationUs) {
+    adDurationsUs[adIndex] = adDurationUs;
+    int nextAdIndex = (adIndex + 1) % adDurationsUs.length;
+    if (adDurationsUs[nextAdIndex] == 0) {
+      // Propagate the remaining duration to the next ad.
+      adDurationsUs[nextAdIndex] = max(0, totalDurationUs - adDurationUs);
+    }
+    return adDurationsUs;
+  }
+
   /**
    * Splits an {@link AdPlaybackState} into a separate {@link AdPlaybackState} for each period of a
    * content timeline. Ad group times are expected to not take previous ad duration into account and
@@ -304,7 +394,7 @@ import java.util.Set;
       }
       // The ad group start timeUs is in content position. We need to add the ad
       // duration before the ad group to translate the start time to the position in the period.
-      long adGroupDurationUs = getTotalDurationUs(adGroup.durationsUs);
+      long adGroupDurationUs = sum(adGroup.durationsUs);
       long elapsedAdGroupAdDurationUs = 0;
       for (int j = periodIndex; j < contentTimeline.getPeriodCount(); j++) {
         contentTimeline.getPeriod(j, period, /* setIds= */ true);
@@ -375,13 +465,5 @@ import java.util.Set;
     return adPlaybackState;
   }
 
-  private static long getTotalDurationUs(long[] durationsUs) {
-    long totalDurationUs = 0;
-    for (long adDurationUs : durationsUs) {
-      totalDurationUs += adDurationUs;
-    }
-    return totalDurationUs;
-  }
-
   private ImaUtil() {}
 }
diff --git a/extensions/ima/src/test/java/com/google/android/exoplayer2/ext/ima/ImaUtilTest.java b/extensions/ima/src/test/java/com/google/android/exoplayer2/ext/ima/ImaUtilTest.java
index a8a6091327..aaf962a195 100644
--- a/extensions/ima/src/test/java/com/google/android/exoplayer2/ext/ima/ImaUtilTest.java
+++ b/extensions/ima/src/test/java/com/google/android/exoplayer2/ext/ima/ImaUtilTest.java
@@ -24,6 +24,7 @@ import androidx.test.ext.junit.runners.AndroidJUnit4;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.source.ads.AdPlaybackState;
+import com.google.android.exoplayer2.source.ads.ServerSideAdInsertionUtil;
 import com.google.android.exoplayer2.testutil.FakeTimeline;
 import com.google.common.collect.ImmutableMap;
 import org.junit.Test;
@@ -503,4 +504,224 @@ public class ImaUtilTest {
       assertThat(periodAdPlaybackState.adsId).isEqualTo("adsId");
     }
   }
+
+  @Test
+  public void expandAdGroupPlaceHolder_expandWithFirstAdInGroup_correctExpansion() {
+    AdPlaybackState adPlaybackState =
+        ServerSideAdInsertionUtil.addAdGroupToAdPlaybackState(
+            AdPlaybackState.NONE,
+            /* fromPositionUs= */ 0,
+            /* contentResumeOffsetUs= */ 0,
+            /* adDurationsUs...= */ 30_000_000);
+
+    adPlaybackState =
+        ImaUtil.expandAdGroupPlaceholder(
+            /* adGroupIndex= */ 0,
+            /* adGroupDurationUs= */ 30_000_000,
+            /* adIndexInAdGroup= */ 0,
+            /* adDurationUs= */ 10_000_000,
+            /* adsInAdGroupCount= */ 3,
+            adPlaybackState);
+
+    AdPlaybackState.AdGroup adGroup = adPlaybackState.getAdGroup(/* adGroupIndex= */ 0);
+    assertThat(adGroup.count).isEqualTo(3);
+    assertThat(adGroup.durationsUs[0]).isEqualTo(10_000_000);
+    assertThat(adGroup.durationsUs[1]).isEqualTo(20_000_000);
+    assertThat(adGroup.durationsUs[2]).isEqualTo(0);
+  }
+
+  @Test
+  public void expandAdGroupPlaceHolder_expandWithMiddleAdInGroup_correctExpansion() {
+    AdPlaybackState adPlaybackState =
+        ServerSideAdInsertionUtil.addAdGroupToAdPlaybackState(
+            AdPlaybackState.NONE,
+            /* fromPositionUs= */ 0,
+            /* contentResumeOffsetUs= */ 0,
+            /* adDurationsUs...= */ 30_000_000);
+
+    adPlaybackState =
+        ImaUtil.expandAdGroupPlaceholder(
+            /* adGroupIndex= */ 0,
+            /* adGroupDurationUs= */ 30_000_000,
+            /* adIndexInAdGroup= */ 1,
+            /* adDurationUs= */ 10_000_000,
+            /* adsInAdGroupCount= */ 3,
+            adPlaybackState);
+
+    AdPlaybackState.AdGroup adGroup = adPlaybackState.getAdGroup(/* adGroupIndex= */ 0);
+    assertThat(adGroup.count).isEqualTo(3);
+    assertThat(adGroup.durationsUs[0]).isEqualTo(0);
+    assertThat(adGroup.durationsUs[1]).isEqualTo(10_000_000);
+    assertThat(adGroup.durationsUs[2]).isEqualTo(20_000_000);
+  }
+
+  @Test
+  public void expandAdGroupPlaceHolder_expandWithLastAdInGroup_correctDurationWrappedAround() {
+    AdPlaybackState adPlaybackState =
+        ServerSideAdInsertionUtil.addAdGroupToAdPlaybackState(
+            AdPlaybackState.NONE,
+            /* fromPositionUs= */ 0,
+            /* contentResumeOffsetUs= */ 0,
+            /* adDurationsUs...= */ 30_000_000);
+
+    adPlaybackState =
+        ImaUtil.expandAdGroupPlaceholder(
+            /* adGroupIndex= */ 0,
+            /* adGroupDurationUs= */ 30_000_000,
+            /* adIndexInAdGroup= */ 2,
+            /* adDurationUs= */ 10_000_000,
+            /* adsInAdGroupCount= */ 3,
+            adPlaybackState);
+
+    AdPlaybackState.AdGroup adGroup = adPlaybackState.getAdGroup(/* adGroupIndex= */ 0);
+    assertThat(adGroup.count).isEqualTo(3);
+    assertThat(adGroup.durationsUs[0]).isEqualTo(20_000_000);
+    assertThat(adGroup.durationsUs[1]).isEqualTo(0);
+    assertThat(adGroup.durationsUs[2]).isEqualTo(10_000_000);
+  }
+
+  @Test
+  public void expandAdGroupPlaceHolder_expandSingleAdInAdGroup_noExpansionCorrectDuration() {
+    AdPlaybackState adPlaybackState =
+        ServerSideAdInsertionUtil.addAdGroupToAdPlaybackState(
+            AdPlaybackState.NONE,
+            /* fromPositionUs= */ 0,
+            /* contentResumeOffsetUs= */ 0,
+            /* adDurationsUs...= */ 30_000_000);
+
+    adPlaybackState =
+        ImaUtil.expandAdGroupPlaceholder(
+            /* adGroupIndex= */ 0,
+            /* adGroupDurationUs= */ 30_000_000,
+            /* adIndexInAdGroup= */ 0,
+            /* adDurationUs= */ 10_000_000,
+            /* adsInAdGroupCount= */ 1,
+            adPlaybackState);
+
+    AdPlaybackState.AdGroup adGroup = adPlaybackState.getAdGroup(/* adGroupIndex= */ 0);
+    assertThat(adGroup.count).isEqualTo(1);
+    assertThat(adGroup.durationsUs[0]).isEqualTo(10_000_000);
+  }
+
+  @Test
+  public void expandAdGroupPlaceHolder_singleAdInAdGroupOverLength_correctsAdDuration() {
+    AdPlaybackState adPlaybackState =
+        ServerSideAdInsertionUtil.addAdGroupToAdPlaybackState(
+            AdPlaybackState.NONE,
+            /* fromPositionUs= */ 0,
+            /* contentResumeOffsetUs= */ 0,
+            /* adDurationsUs...= */ 10_000_001);
+
+    adPlaybackState =
+        ImaUtil.expandAdGroupPlaceholder(
+            /* adGroupIndex= */ 0,
+            /* adGroupDurationUs= */ 10_000_000,
+            /* adIndexInAdGroup= */ 0,
+            /* adDurationUs= */ 10_000_000,
+            /* adsInAdGroupCount= */ 1,
+            adPlaybackState);
+
+    AdPlaybackState.AdGroup adGroup = adPlaybackState.getAdGroup(/* adGroupIndex= */ 0);
+    assertThat(adGroup.count).isEqualTo(1);
+    assertThat(adGroup.durationsUs[0]).isEqualTo(10_000_000);
+  }
+
+  @Test
+  public void expandAdGroupPlaceHolder_initialDurationTooLarge_overriddenWhenExpanded() {
+    AdPlaybackState adPlaybackState =
+        ServerSideAdInsertionUtil.addAdGroupToAdPlaybackState(
+            AdPlaybackState.NONE,
+            /* fromPositionUs= */ 0,
+            /* contentResumeOffsetUs= */ 0,
+            /* adDurationsUs...= */ 30_000_000);
+
+    adPlaybackState =
+        ImaUtil.expandAdGroupPlaceholder(
+            /* adGroupIndex= */ 0,
+            /* adGroupDurationUs= */ 20_000_000,
+            /* adIndexInAdGroup= */ 1,
+            /* adDurationUs= */ 10_000_000,
+            /* adsInAdGroupCount= */ 2,
+            adPlaybackState);
+
+    AdPlaybackState.AdGroup adGroup = adPlaybackState.getAdGroup(/* adGroupIndex= */ 0);
+    assertThat(adGroup.count).isEqualTo(2);
+    assertThat(adGroup.durationsUs[0]).isEqualTo(10_000_000);
+    assertThat(adGroup.durationsUs[1]).isEqualTo(10_000_000);
+  }
+
+  @Test
+  public void insertAdDurationInAdGroup_correctDurationAndPropagation() {
+    AdPlaybackState adPlaybackState =
+        ServerSideAdInsertionUtil.addAdGroupToAdPlaybackState(
+            AdPlaybackState.NONE,
+            /* fromPositionUs= */ 0,
+            /* contentResumeOffsetUs= */ 0,
+            /* adDurationsUs...= */ 10_000_000,
+            20_000_000,
+            0);
+
+    adPlaybackState =
+        ImaUtil.updateAdDurationInAdGroup(
+            /* adGroupIndex= */ 0,
+            /* adIndexInAdGroup= */ 1,
+            /* adDurationUs= */ 15_000_000,
+            adPlaybackState);
+
+    AdPlaybackState.AdGroup adGroup = adPlaybackState.getAdGroup(0);
+    assertThat(adGroup.count).isEqualTo(3);
+    assertThat(adGroup.durationsUs[0]).isEqualTo(10_000_000);
+    assertThat(adGroup.durationsUs[1]).isEqualTo(15_000_000);
+    assertThat(adGroup.durationsUs[2]).isEqualTo(5_000_000);
+  }
+
+  @Test
+  public void insertAdDurationInAdGroup_insertLast_correctDurationAndPropagation() {
+    AdPlaybackState adPlaybackState =
+        ServerSideAdInsertionUtil.addAdGroupToAdPlaybackState(
+            AdPlaybackState.NONE,
+            /* fromPositionUs= */ 0,
+            /* contentResumeOffsetUs= */ 0,
+            /* adDurationsUs...= */ 0,
+            10_000_000,
+            20_000_000);
+
+    adPlaybackState =
+        ImaUtil.updateAdDurationInAdGroup(
+            /* adGroupIndex= */ 0,
+            /* adIndexInAdGroup= */ 2,
+            /* adDurationUs= */ 15_000_000,
+            adPlaybackState);
+
+    AdPlaybackState.AdGroup adGroup = adPlaybackState.getAdGroup(0);
+    assertThat(adGroup.count).isEqualTo(3);
+    assertThat(adGroup.durationsUs[0]).isEqualTo(5_000_000);
+    assertThat(adGroup.durationsUs[1]).isEqualTo(10_000_000);
+    assertThat(adGroup.durationsUs[2]).isEqualTo(15_000_000);
+  }
+
+  @Test
+  public void insertAdDurationInAdGroup_allDurationsSetAlready_setDurationNoPropagation() {
+    AdPlaybackState adPlaybackState =
+        ServerSideAdInsertionUtil.addAdGroupToAdPlaybackState(
+            AdPlaybackState.NONE,
+            /* fromPositionUs= */ 0,
+            /* contentResumeOffsetUs= */ 0,
+            /* adDurationsUs...= */ 5_000_000,
+            10_000_000,
+            20_000_000);
+
+    adPlaybackState =
+        ImaUtil.updateAdDurationInAdGroup(
+            /* adGroupIndex= */ 0,
+            /* adIndexInAdGroup= */ 1,
+            /* adDurationUs= */ 5_000_000,
+            adPlaybackState);
+
+    AdPlaybackState.AdGroup adGroup = adPlaybackState.getAdGroup(0);
+    assertThat(adGroup.count).isEqualTo(3);
+    assertThat(adGroup.durationsUs[0]).isEqualTo(5_000_000);
+    assertThat(adGroup.durationsUs[1]).isEqualTo(5_000_000);
+    assertThat(adGroup.durationsUs[2]).isEqualTo(20_000_000);
+  }
 }